Write Json Data -

public class Address {
    String city;
    int pin;

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public int getPin() {
        return pin;
    }

    public void setPin(int pin) {
        this.pin = pin;
    }

    public Address() {
    }
   
}




====================


public class Employee {
    String name;
    int age;
    Address address;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public Employee() {
    }
   
}

====================

public class WriteJson {
    public static void main(String[] args) {
        Address a=new Address();
        a.setCity("Nagpur");
        a.setPin(23);
        Employee e=new Employee();
        e.setName("raju");
        e.setAge(12);
        e.setAddress(a);
       
        Address a1=new Address();
        a1.setCity("Pune");
        a1.setPin(32);
        Employee e1=new Employee();
        e1.setName("Sachin");
        e1.setAge(12);
        e1.setAddress(a1);
       
        Gson g=new Gson();
        System.out.println(g.toJson(e));
       
        ArrayList<Employee> empList=new ArrayList<>();
        empList.add(e);
        empList.add(e1);
       
         System.out.println(g.toJson(empList));
       
       
    }
}